Currently, known pistons used in hydraulic cylinders for tractors, construction, mining, earth moving equipment, and the like, are made from high strength or hardened metallic materials. One reason for this is that those materials are able to withstand the compressive stress conditions acting on the pistons caused by high torque on the nuts and/or bolts used to fasten the pistons to piston rods for axial movement in the hydraulic cylinders. High strength or hardened metallic materials are also used because they are able to withstand the high pressure working conditions. However, a disadvantage of high strength and hardened metallic materials is that they are costly, due both to the cost of the metallic materials themselves, and the cost of machining and finishing the metallic pistons. Also, the fasteners used for fastening the pistons to the piston rods are typically required to be tightened to high torque levels, necessitating special tools for that purpose.
Reference Stoll et al. U.S. Pat. No. 4,762,052, issued Aug. 9, 1988; Leigh-Monstevens et al. U.S. Pat. No. 4,831,916, issued May 23, 1989; and Reinartz et al. GB 2222213, published Feb. 28, 1990, which disclose various piston constructions made at least substantially from plastic materials. However, U.S. Pat. No. 4,762,052 and U.S. Pat. No. 4,831,916, disclose piston constructions which still require metallic members at some locations thereon. GB 2222213 discloses a master cylinder and piston operable therein made from plastic, but which is used in a relatively low pressure, low torque application for actuation of an automotive clutch.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.